Monomolecular film modified copper current collector for negative-electrode-free lithium metal battery and preparation method of monomolecular film modified copper current collector

Abstract

The invention discloses a monomolecular film modified copper current collector for a negative-electrode-free lithium metal battery and a preparation method of the monomolecular film modified copper current collector, the copper current collector is soaked in an organic molecule solution containing polar groups, and then an ordered monomolecular film is formed on the surface of the copper current collector through self-assembly. According to the method for optimizing the performance of the lithium metal without the negative electrode, a layer of self-assembled monomolecular film with a specific terminal group is formed on the surface of a copper current collector through ordered arrangement, so that electrolyte is controllably decomposed, a lithium fluoride-rich solid electrolyte interface film is generated, lithium ion transmission is accelerated, and growth of lithium dendrites is inhibited; therefore, the negative-electrode-free lithium metal battery with long service life and long stability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of negative electrode-free lithium metal battery technology, specifically relating to a single-molecule film modified copper current collector for negative electrode-free lithium metal batteries and its preparation method. Background Technology

[0002] Currently, lithium-ion batteries primarily use graphite as the anode material, but its energy density is approaching its theoretical limit. Lithium metal, on the other hand, possesses an extremely high theoretical specific capacity. Compared to traditional lithium-ion batteries using graphite as the anode material, lithium metal batteries using lithium metal as the anode material exhibit significantly higher energy density.

[0003] However, the high reactivity of lithium metal with the electrolyte can trigger irreversible lithium dendrite formation and dead lithium formation, resulting in an unstable solid-electrolyte interface, leading to low coulombic efficiency and poor cycle life. To address these issues, electrodeless lithium metal batteries are considered a superior solution. Electrodeless lithium metal batteries use copper or similar materials as the negative electrode current collector. Because they initially contain no metallic lithium, they possess excellent chemical stability, higher safety, and cost advantages. However, the surface of untreated copper current collectors is uneven, easily inducing uneven lithium deposition, forming lithium dendrites, which can then puncture the separator and cause short circuits. Therefore, modifying the surface of the copper current collector to regulate lithium deposition behavior is key to achieving high-performance electrodeless lithium metal batteries. For example, Wang et al. proposed a shape-change-free, lithium-free anode composed of a zinc oxide substrate and a surface-coated lithium phosphorus nitride layer, which can effectively regulate the reversible lithium deposition and stripping process. The zinc oxide substrate, with its ample cavities and lithiophilic sites, promotes uniform lithium deposition and stripping, while the lithium phosphorus nitride layer protects the solid-electrolyte interface from mechanical and electrochemical damage, maintaining its stability. Therefore, the entire negative electrode structure effectively maintains shape stability under long-term cycling and high-rate conditions (Advanced Materials, 2025, 37, 18). Wondimkun et al. prepared a lithiophilic Ag@PDA-GO composite current collector via spin coating, whose synergistic effect enabled uniform lithium deposition. This material significantly reduced the lithium nucleation barrier in a carbonate electrolyte containing fluorinated ethylene carbonate, at a concentration of 0.5 mA cm⁻¹. -2 After 60 cycles of current density cycling, LiNi was matched. 1 / 3 Mn 1 / 3Co 1 / 3The full-cell capacity retention rate of the O2 cathode reached 55.7% (Energy Storage Materials, 2021, 35, 3). Patent CN 119650579 A proposes coating a copper foil surface with a PTFE-containing primer slurry, drying and cutting it into a specific shape, and then assembling it into a battery. The formed SEI film has a dual function of promoting uniform lithium metal deposition and preventing the reaction between lithium metal and electrolyte, greatly improving the stability of electrodeless lithium metal batteries. The aforementioned modification method uses simple physical modification means, but the bonding strength between the modified layer and the copper current collector is insufficient. During lithium deposition and stripping cycles, the modified layer is prone to cracking or even peeling off from the current collector surface. At the same time, the drastic lithium volume change often exceeds the coating flexibility limit, seriously restricting the cycle life of electrodeless lithium metal batteries. Moreover, such modification processes are highly complex, increasing production costs and reducing production efficiency. Therefore, developing a negative electrode current collector that combines strong interfacial bonding, structural stability, long cycle life, and simple preparation process has become a technical bottleneck that urgently needs to be overcome in the field of electrodeless lithium metal batteries. Summary of the Invention

[0004] To avoid the shortcomings of the existing technology, the present invention provides a monomolecular film modified copper current collector for electrodeless lithium metal batteries and its preparation method, aiming to enable the assembled electrodeless lithium metal battery to quickly and stably form a solid electrolyte interface film, thereby having high electrochemical stability, high electronic conductivity and first coulombic efficiency, and improving the overall electrochemical performance of the material.

[0005] To achieve its objectives, the present invention employs the following technical solution: A method for preparing a monolayer modified copper current collector for use in electrodeless lithium metal batteries comprises the following steps: Step 1: Dissolve organic molecules containing polar groups in a solvent to obtain a modified solution; Step 2: Immerse the copper current collector, which has been cleaned with anhydrous ethanol, in the modification solution; Step 3: Dry the impregnated copper current collector to obtain a monomolecular film modified copper current collector.

[0006] Furthermore, in step 2, the thickness of the copper current collector is 6-20 µm.

[0007] Further, in step 1, the polar group is a carboxyl group, an amino group, a thiol group, or a fluorine-containing group, specifically including at least one of the following molecules: malonic acid, succinic acid, etc., containing carboxyl groups; β-alanine, glycine, etc., containing amino groups; (3-mercaptopropyl)trimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, etc., containing thiol groups; perfluorododecyl polysiloxane, perfluorodecyltriethoxysilane, etc., containing fluorine-containing groups. The orderly arrangement of the terminal groups of the monolayer can control the decomposition of fluorine-containing components in the electrolyte to guide the uniform deposition of lithium metal, with the group source containing polar groups being optimal.

[0008] Further, in step 1, the solvent is at least one of ethanol, methanol, aqueous ethanol solution, and aqueous methanol solution.

[0009] Furthermore, in step 1, the concentration of organic molecules containing polar groups in the modified solution is 2.5-10 g / L.

[0010] Furthermore, in step 2, the immersion temperature of the copper current collector is 28-50℃, and the immersion time is 1-10 h.

[0011] Furthermore, in step 3, the drying temperature is 30-50℃ and the drying time is 1-10 h.

[0012] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. The present invention optimizes the performance of electrodeless lithium metal batteries by forming a self-assembled monomolecular film with specific terminal groups on the surface of a copper current collector, thereby enabling the electrolyte to decompose in a controlled manner and generate a lithium fluoride-rich solid electrolyte interface film, accelerating lithium-ion transport and inhibiting the growth of lithium dendrites. The monomolecular film technology is used to modify and regulate the formation of the solid electrolyte interface film of the negative electrode and the deposition / stripping of lithium metal in electrodeless lithium metal batteries, thereby achieving a high-lifetime and long-stability electrodeless lithium metal battery.

[0013] 2. The monomolecular film constructed on the surface of the copper current collector in this invention has a thickness of less than 1 µm, which is significantly reduced compared to traditional coating-type modification layers, thus reducing energy density loss. The introduction of polar groups in the copper current collector enhances the interaction with lithium ions and effectively reduces the overpotential for lithium nucleation. The orderly arrangement of terminal groups in the monomolecular film effectively controls the decomposition of fluorine-containing components in the electrolyte, promoting the formation of a stable solid electrolyte interface layer with high ionic conductivity on the negative electrode surface. This reduces the charge transport resistance at the interface, promotes lithium ion transport and nucleation, and redistributes the lithium ion transport pathway, thereby inhibiting the growth of lithium dendrites and improving the cycle stability of the battery.

[0014] 3. This invention uses a simple impregnation method to chemically modify copper current collectors, thereby constructing a monomolecular film on the surface of the copper current collector. The process is simple, easy to implement, and environmentally friendly, making it suitable for industrial production. Attached Figure Description

[0015] Figure 1 This is the Raman spectrum of the copper current collector surface modified with a monolayer prepared in Example 1 of the present invention.

[0016] Figure 2 Half-cells assembled with unmodified copper current collectors and monolayer modified copper current collectors obtained in Examples 1 and 4 were used at a current density of 1 mA cm⁻¹. -2 Lithium plating amount 0.5 mAh cm -2 Voltage distribution diagram of initial lithium deposition.

[0017] Figure 3 For a current density of 1 mA cm -2 The lithium plating amount is 0.5 mAh cm⁻¹ -2 The coulombic efficiency of half-cells assembled with monolayer modified current collectors under different immersion temperatures (30℃, 50℃) and different modification solution concentrations (2.5 g / L, 5.0 g / L, 7.5 g / L) is plotted for lithium plating / stripping.

[0018] Figure 4 The monolayer modified copper current collector prepared in Example 4 ( Figure 4 (a) and (c) in the above) and unmodified copper current collector ( Figure 4 SEM images of the surface after 10 and 50 lithium plating / stripping cycles (b) and (d) in the image.

[0019] Figure 5 The graph shows the cycling performance of CR2032 coin cells assembled with monolayer modified copper current collectors and unmodified copper current collectors prepared in Examples 1 and 4 at a current density of 0.5 C. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept or exceed the scope defined by the claims, all of which should fall within the protection scope of the present invention.

[0021] Example 1 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.0625 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 2.5 g / L.

[0022] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; then immerse the cleaned copper foil in a 30°C modification solution for 10 h.

[0023] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0024] Example 2 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.1250 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 5.0 g / L.

[0025] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; then immerse the cleaned copper foil in a 30°C modification solution for 10 h.

[0026] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0027] Example 3 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.1875 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 7.5 g / L.

[0028] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; then immerse the cleaned copper foil in a 30°C modification solution for 10 h.

[0029] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0030] Example 4 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.0625 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 2.5 g / L.

[0031] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; immerse the cleaned copper foil in a 50°C modification solution for 1 h.

[0032] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0033] Example 5 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.1250 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 5.0 g / L.

[0034] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; immerse the cleaned copper foil in a 50°C modification solution for 1 h.

[0035] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0036] Example 6 In this embodiment, a monolayer modified copper current collector was prepared according to the following steps: Step 1: Dissolve 0.1850 g of succinic acid in 25 mL of ethanol to obtain a modified solution with a concentration of 7.5 g / L.

[0037] Step 2: Cut a 10 µm thick copper foil into pieces with a diameter of 14 mm and wipe them with anhydrous ethanol; immerse the cleaned copper foil in a 50°C modification solution for 1 h.

[0038] Step 3: Dry the impregnated copper foil at 50°C for 1 hour to obtain a monomolecular film modified copper current collector.

[0039] In an argon (Ar)-filled glove box, half-cells were assembled in the following order: negative electrode shell - lithium sheet - electrolyte - separator - monolayer modified copper current collector. The separator was Celgard, and the electrolyte was 1 M lithium bis(trifluoromethanesulfonyl)imide dissolved in 1,3-dioxolane / 1,2-ethylene glycol dimethyl ether (volume ratio 1:1) with 2 wt% lithium nitrate as an additive.

[0040] Figure 1 The image shows the Raman spectrum of the monolayer modified copper current collector obtained in Example 1. The results indicate that the current is highest at 1630 and 1440 cm⁻¹. -1 The peaks at 606 cm⁻¹ represent the antisymmetric and symmetric stretching vibrations of the carboxylate group, respectively. -1 The peak at 1188 cm⁻¹ represents the Cu-O group. -1 The peak at that location represents a CO group. This confirms that the surface of the copper current collector was successfully modified with HOOC(CH2)2COOH molecules, resulting in a Cu-OOC(CH2)2COOH current collector.

[0041] Figure 2 Two types of Cu-OOC(CH2)2COOH current collectors were assembled into half-cells at a current density of 1 mA cm⁻¹, prepared by immersing copper foil current collectors in a modified solution at a concentration of 2.5 g / L at 30°C for 10 h (sample obtained in Example 1) and at 50°C for 1 h (sample obtained in Example 4). -2 Lithium plating amount 0.5 mAh cm -2 The voltage distribution diagram of initial lithium deposition is shown. It can be seen that, under the same modification solution concentration, the monolayer modified copper current collector obtained by immersion at 50℃ for 1 h exhibits the lowest nucleation overpotential (7.7 mV), far lower than the 21.1 mV of the Cu foil. Simultaneously, the monolayer modified copper current collector obtained by immersion at 30℃ for 10 h also exhibits a much lower nucleation overpotential (10.2 mV) than the Cu foil. This demonstrates that the prepared Cu-OOC(CH2)2COOH can lower the energy barrier for lithium nucleation, induce uniform lithium metal deposition, reduce the formation of lithium dendrites and dead lithium, thereby improving the cycle life of the battery. These advantages are also reflected in the improvement of the initial coulombic efficiency, proving that the Cu-OOC(CH2)2COOH monolayer can effectively reduce the loss of active lithium.

[0042] Figure 3 For a current density of 1 mA cm -2 The lithium plating amount is 0.5 mAh cm⁻¹ -2 The image shows the coulombic efficiency (COP) of lithium plating / stripping for half-cells assembled with monolayer modified copper current collectors obtained under different immersion temperatures (30℃, 50℃) and different modification solution concentrations (2.5 g / L, 5.0 g / L, 7.5 g / L). The half-cell using pure Cu foil as the current collector showed drastic fluctuations after only 50 cycles. In stark contrast, the monolayer modified copper current collectors obtained under the low-concentration atmosphere (2.5 g / L) under both immersion conditions of 30℃ for 10 h and 50℃ for 1 h exhibited long-term stability exceeding 300 cycles, with average CE greater than 97%. Furthermore, under the same immersion temperature, the overall electrochemical performance of both was superior to that at concentrations of 5.0 g / L and 7.5 g / L. At the same concentration, the monolayer modified copper current collector obtained by immersing copper foil at 50℃ for 1 h showed varying degrees of optimization compared to the monolayer modified copper current collector obtained by immersing at 30℃ for 10 h. The final experimental scheme was carried out using a copper current collector (sample of Example 4) that was immersed in 2.5 g / L succinic acid-ethanol solution at 50°C for 1 h, which had the best overall performance.

[0043] Figure 4The images show SEM images of the surfaces of the monolayer-modified copper current collector and the unmodified copper current collector prepared in Example 4 after 10 and 50 lithium deposition / stripping cycles. The results show that after 10 and 50 lithium deposition / stripping cycles, the Cu-OOC(CH2)2COOH current collector leaves a smooth surface. Figure 4 In contrast to (a) and (c) in the above examples, under the same number of cycles, a large amount of irregularly shaped deposits still remain on the surface of the unmodified Cu current collector. Figure 4 (b) and (d) in the text. It can be seen that the copper foil modified with a monolayer can indeed improve the morphology of lithium deposition and the formation state of the solid electrolyte interface layer.

[0044] Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene (PTFE) were weighed in a mass ratio of 95:5:5. PTFE was first added to a certain amount of N-methyl-2-pyrrolidone and stirred until completely dissolved. Lithium iron phosphate and conductive carbon black were then ground uniformly and added to the solution, and stirred for 10 hours to obtain a uniform slurry with a solid content of approximately 43%. The slurry was uniformly coated onto the surface of carbon-coated aluminum foil using a scraper. After drying, rolling, cutting, and weighing, the foil was placed in a glove box as a positive electrode. Using the monomolecular film-modified copper current collector obtained in Examples 1 and 4 as the negative electrode, Celgard as the separator, and 1 M lithium bis(trifluoromethanesulfonyl)imide dissolved in 1,3-dioxolane / 1,2-ethylene glycol dimethyl ether (volume ratio 1:1) as the electrolyte, a CR2032 coin cell was assembled in an argon glove box. A constant current charge-discharge experiment was then conducted on this cell at room temperature, and the results are as follows: Figure 5 As shown, the battery assembled using the monolayer-modified copper current collector of Example 4 has an initial discharge specific capacity of 160.47 mAh g⁻¹. -1 After 100 cycles at a 0.5 C ratio, the capacity retention rate is 40.43%.

[0045] The above description is merely a preferred embodiment of the present invention, and while it is quite specific and detailed, it should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and equivalent substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a monolayer modified copper current collector for use in electrodeless lithium metal batteries, characterized in that, Follow these steps: Step 1: Dissolve organic molecules containing polar groups in a solvent to obtain a modified solution; Step 2: Immerse the cleaned copper current collector in the modification solution; Step 3: Dry the impregnated copper current collector to obtain a monomolecular film modified copper current collector.

2. The preparation method according to claim 1, characterized in that: In step 2, the thickness of the copper current collector is 6-20 µm.

3. The preparation method according to claim 1, characterized in that: In step 1, the polar group is a carboxyl group, an amino group, a thiol group, or a fluorine-containing group.

4. The preparation method according to claim 1, characterized in that, In step 1, the organic molecule containing a polar group is at least one of the following molecules: malonic acid or succinic acid containing a carboxyl group, β-alanine or glycine containing an amino group, (3-mercaptopropyl)trimethoxysilane or 3-mercaptopropylmethyldimethoxysilane containing a thiol group, or perfluorododecyl polysiloxane or perfluorodecyltriethoxysilane containing a fluorine group.

5. The preparation method according to claim 1, characterized in that: In step 1, the solvent is at least one of ethanol, methanol, aqueous ethanol solution, and aqueous methanol solution, and the concentration of the organic molecules containing polar groups in the modified solution is 0.25-10 g / L.

6. The preparation method according to claim 1, characterized in that: In step 2, the immersion temperature of the copper current collector is 28-50℃, and the immersion time is 1-10 h.

7. The preparation method according to claim 1, characterized in that: In step 3, the drying temperature is 30-50℃ and the drying time is 1-10 h.

8. A monolayer modified copper current collector prepared by the preparation method according to any one of claims 1 to 7.

9. A cathodeless lithium metal battery using the monomolecular film modified copper current collector as described in claim 8 as the cathode.

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